Polarizers for image sensor devices

ABSTRACT

The present disclosure is directed to a method of forming a polarization grating structure (e.g., polarizer) as part of a grid structure of a back side illuminated image sensor device. For example, the method includes forming a layer stack over a semiconductor layer with radiation-sensing regions. Further, the method includes forming grating elements of one or more polarization grating structures within a grid structure, where forming the grating elements includes (i) etching the layer stack to form the grid structure and (ii) etching the layer stack to form grating elements oriented to a polarization angle.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a continuation of U.S. Non-Provisional patentapplication Ser. No. 15/964,288, filed on Apr. 27, 2018 and titled“Polarizers for Image Sensor Devices,” which claims the benefit of U.S.Provisional Patent Application No. 62/586,277, filed on Nov. 15, 2017and titled “Polarizers for Image Sensor Devices.” The entire contents ofboth applications are incorporated by reference herein in theirentireties.

BACKGROUND

Semiconductor image sensors are used to sense radiation, such as light.Complementary metal-oxide-semiconductor (CMOS) image sensors (CIS) andcharge-coupled device (CCD) sensors are used in various applicationssuch as digital still camera or mobile phone camera applications. Thesedevices utilize an array of pixels (which can include photodiodes,transistors, and other components) in a substrate to absorb (e.g.,sense) radiation that is projected toward the substrate and convert thesensed radiation into electrical signals. A hack side illuminated imagesensor device is one type of image sensor device that can detect lightfrom the back side.

BRIEF DESCRIPTION OF THE DRAWINGS

Aspects of the present disclosure are best understood from the followingdetailed description when read with the accompanying figures. It isnoted that, in accordance with the common practice in the industry,various features are not drawn to scale. In fact, the dimensions of thevarious features may be arbitrarily increased or reduced for clarity ofillustration and discussion.

FIG. 1 is a cross-sectional view of a backside illuminated image sensordevice, according to some embodiments.

FIG. 2 is a top view of a composite grid structure with color filters,according to some embodiments.

FIG. 3 is a flow chart of a method for forming a polarization gratingstructure in a composite grid structure of a backside illuminated imagesensor device, according to some embodiments.

FIGS. 4-6 are cross-sectional views of a partially fabricated backsideilluminated image sensor device during formation of a polarizationgrating structure, according to some embodiments.

FIGS. 7A-D are top views of polarization grating structures with gratingelements oriented in different polarization angles, according to someembodiments.

FIG. 8 is a cross-sectional view of a partially fabricated backsideilluminated image sensor device after deposition of a passivation layer,according to some embodiments.

FIG. 9 is a cross-sectional view of a backside illuminated image sensordevice with a polarization grating structure, according to someembodiment.

FIGS. 10-13 are top views of composite grid structures with polarizationgrating structures in different arrangements, according to someembodiments.

DETAILED DESCRIPTION

The following disclosure provides many different embodiments, orexamples, for implementing different features of the provided subjectmatter. Specific examples of components and arrangements are describedbelow to simplify the present disclosure. These are, of course, merelyexamples and are not intended to be limiting. For example, the formationof a first feature over a second feature in the description that followsmay include embodiments in which the first and second features areformed in direct contact, and may also include embodiments in whichadditional features are disposed between the first and second features,such that the first and second features are not in direct contact.

Further, spatially relative terms, such as “beneath,” “below,” “lower,”“above,” “upper” and the like, may be used herein for ease ofdescription to describe one element or feature's relationship to anotherelement(s) or feature(s) as illustrated in the figures. The spatiallyrelative terms are intended to encompass different orientations of thedevice in use or operation in addition to the orientation depicted inthe figures. The apparatus may be otherwise oriented (rotated 90 degreesor at other orientations) and the spatially relative descriptors usedherein may likewise be interpreted accordingly.

The term “nominal” as used herein refers to a desired, or target, valueof a characteristic or parameter for a component or a process operation,set during the design phase of a product or a process, together with arange of values above and/or below the desired value. The range ofvalues can be due to slight variations in manufacturing processes ortolerances.

The term “substantially” as used herein indicates the value of a givenquantity varies by ±5% of the value.

The term “about” as used herein indicates the value of a given quantitythat can vary based on a particular technology node associated with thesubject semiconductor device. Based on the particular technology node,the term “about” can indicate a value of a given quantity that varieswithin, for example, 10-30% of the value (e.g., ±10%, ±20%, or ±30% ofthe value).

Semiconductor image sensor devices are used to sense electromagneticradiation, such as light (e.g., visible light). Complementarymetal-oxide-semiconductor (CMOS) image sensors (CIS) and charge-coupleddevice (CCD) sensors can be used in various applications, such asdigital still camera or mobile phone camera applications. These devicesutilize an array of pixels (which can include photodiodes, transistors,and other components) in a substrate to absorb (e.g., sense) radiationthat is projected toward the substrate. The absorbed radiation can beconverted by the photodiodes (in the pixel) into electrical signals,such as charge or current, that can be further analyzed and/or processedby other modules of the image sensor device.

One type of image sensor device is a back side illuminated image sensordevice. In a back side illuminated image sensor device, color filtersand micro-lenses are positioned on the back side of a substrate (e.g.,on an opposite side of the substrate's circuitry), so that the imagesensor device can collect light with minimal or no obstructions. As aresult, back side illuminated image sensor devices are configured todetect light from the back side of the substrate, rather than from afront side of the substrate where the color filters and micro-lenses ofthe image sensor device are positioned between the substrate's circuitryand the photodiodes. Compared to front side illuminated image sensordevices, back side illuminated image sensor devices have improvedperformance under low light conditions and higher quantum efficiency(QE) (e.g., photon to electron conversion percentage).

Image sensor devices use color filters to capture color information fromincident light rays. For example, the image sensor devices—through theuse of color filters—can detect the red, green, and blue (RGB) regionsof the visible light spectrum. A composite grid structure, which can befilled with color filter material, can be used to position the colorfilter material above photodiodes of the image sensor device. Thecomposite grid structure can be made in part from an oxide or anotherdielectric material which is transparent to visible light.

Further, the image sensor can also be equipped with external polarizersin order to collect polarization information from incident light.Polarization information can be used in applications such as photographyand filming. However, since the polarizers are external and notintegrated to the composite grid structure, a distance between thepolarizers and the image sensor can be substantial—e.g., relative to thesize of the back side illuminated image sensor device. Thisconfiguration can impact the final product's size and can restrict sizereduction efforts. Further, in order to obtain information on differentpolarization conditions, the external polarizer can rotate, or spin,which can impact polarization data acquisition time.

Various embodiments in accordance with this disclosure provide a methodto integrate one or more polarizers in a composite grid structure of aback side illuminated image sensor device. In some embodiments, thepolarizers are integrated into the composite grid structure by replacingone or more color filters of the composite grid structure with apolarizing grating structure (grid polarizer) within the composite gridstructure. In some examples, the polarizing grating structure canprovide polarization information for incident light along the followingpolarization angles: 0°, 45°, 90° , and/or 135° . However, thesedirections are not limiting and other polarization angles are possible.According to some embodiments, the pitch between the elements (gratingelements) of the polarizing grating structure can range from about 100nanometers (nm) to about 500 nm (e.g., from 100 nm to 500 nm), and thewidth of each grating element can range from about 20 nm to about 300 nm(e.g., from 20 nm to 300 nm), The aforementioned ranges are optimizedbased on the wavelength of the incident light. In some embodiments, thegrating elements of the polarizing grating structure include a samematerial as the composite grid structure. In some embodiments, thegrating elements of the polarizing grating structure include a differentmaterial from the composite grid structure.

FIG. 1 is a simplified cross-sectional view of a back side illuminatedimage sensor device 100, according to some embodiments of the presentdisclosure. Back side illuminated image sensor device 100 includes asemiconductor layer 102 with radiation-sensing areas 104. Semiconductorlayer 102 can include a silicon material doped with a p-type dopant,such as boron. Alternatively, semiconductor layer 102 can includesilicon doped with an n-type dopant, such as phosphorous or arsenic.Semiconductor layer 102 can also include other elementarysemiconductors, such as germanium or diamond. Semiconductor layer 102can optionally include a compound semiconductor and/or an alloysemiconductor. Further, semiconductor layer 102 can include an epitaxiallayer, which may be strained for performance enhancement. Semiconductorlayer 102 can include a silicon-on-insulator (SOI) structure.

Semiconductor layer 102 has a front side (also referred to herein as a“bottom surface”) 106 and a back side (also referred to herein as a “topsurface”) 108. Semiconductor layer 102 has a thickness that can rangefrom about 100 μm to about 3000 μm (e.g., from 100 μm to 3000 μm).

Radiation-sensing regions 104 are formed in semiconductor layer 102.Radiation-sensing regions 104 are configured to sense radiation, such asincident light rays impinging semiconductor layer 102 from back side108. Each of the radiation-sensing regions or radiation-sensing regions104 include a photodiode that can convert photons to charge, accordingto some embodiments of the present disclosure. In some embodiments ofthe present disclosure, radiation-sensing regions 104 can includephotodiodes, transistors, amplifiers, other similar devices, orcombinations thereof. Radiation-sensing regions 104 may also be referredto herein as “radiation-detection devices” or “light-sensors.”

For simplicity, two radiation-sensing regions 104 are illustrated inFIG. 1, but additional radiation-sensing regions 104 can be implementedin semiconductor layer 102. By way of example and not limitation,radiation-sensing regions 104 can be formed using an ion implant processon semiconductor layer 102 from front side 106. Radiation-sensingregions 104 can also be formed by a dopant diffusion process.

Radiation-sensing regions 104 are electrically isolated from each otherwith isolation structures 110. Isolation structures 110 can be trenchesetched into semiconductor layer 102 and filled with a dielectricmaterial, such as silicon oxide, silicon nitride, silicon oxynitride,fluorine-doped silicate glass (FSG), a low-k dielectric material (e.g.,a material with a k value lower than 3.9), and/or a suitable insulatingmaterial. According to some embodiments of the present disclosure,isolation structures 110 on back side 108 of semiconductor layer 102have an anti-reflective coating (ARC) 112. ARC 112 is a liner layer thatcan prevent incoming light rays from being reflected away fromradiation-sensing areas/pixels 104. ARC 112 can include a high-kmaterial (e.g., a material with a k-value lower than 3.9), such ashafnium oxide (HfO₂), tantalum pentoxide (Ta₂O₅), zirconium dioxide(ZrO₂), aluminum oxide (Al₂O₃), or any other high-k material. ARC 112can be deposited using a sputtering process, a chemical vapor deposition(CVD)-based process, an atomic layer deposition (ALD)-based techniques,or any other suitable deposition technique. In some embodiments of thepresent disclosure, the thickness of ARC 112 can range from about 10 Åto about 500 Å (e.g., from 10 Å to 50 Å).

Back side illuminated image sensor device 100 also includes a cappinglayer 114 formed over semiconductor layer 102, such as over ARC 112, asillustrated in FIG. 1. In some embodiments of the present disclosure,capping layer 114 can provide a planar surface on which additionallayers of back side illuminated image sensor device 100 can be formed.Capping layer 114 can include a dielectric material, such as siliconoxide (SiO₂), silicon nitride (Si₃N₄), silicon oxy-nitride (SiON), orany other suitable dielectric material. Further, capping layer 114 canbe deposited using CVD or any other suitable deposition technique. Insome embodiments of the present disclosure, the thickness of cappinglayer 114 can range between about 500 Å and about 2000 Å (e.g., from 500Å to 2000 Å).

Further, back side illuminated image sensor device 100 includes acomposite grid structure 116 formed over capping layer 114. According tosome embodiments of the present disclosure, composite grid structure 116includes cells 118 arranged in columns and rows, where each cell 118 isaligned to a respective radiation-sensing area 104. As mentioned above,cells 118 can receive a red, green, or blue color filter 120.

FIG. 2 is a top view of composite grid structure 116, according to someembodiments. The arrangement of color filters 120 in composite gridstructure 116 can be based on a Bayern pattern. For example, compositegrid structure 116 can include 50% green color filters, 25% red colorfilters and 25% blue color filters, where every other cell 118 ofcomposite grid structure 116 is filled with a different color filter120. However, this is not limiting and neighboring cells 118 can beoccupied (e.g., filled) by the same-color color filter.

Referring to FIG. 1, cells 118 of composite grid structure 116 can beformed by depositing a bottom layer 122 and a top dielectric layer 124and selectively etching away portions of the bottom layer and topdielectric layer to form cells 118. By way of example and notlimitation, composite grid structure 116 can be formed as follows:bottom layer 122 and top dielectric layer 124 can be blanket depositedon capping layer 114; and one or more photolithography and etchoperations can be used to pattern bottom layer 122 and top dielectriclayer 124 to form the sidewalk of cells 118. The photolithography andetch operations can be performed so that each cell 118 of composite gridstructure 116 is aligned to respective radiation-sensing regions 104 ofsemiconductor layer 102. In some embodiments, the sidewall height ofeach cell 118 of composite grid structure 116 can range from about 200nm to about 1000 nm (e.g., from 200 nm to 1000 nm).

Bottom layer 122 of cell 118 can be made of titanium, tungsten,aluminum, or copper. However, bottom layer 122 of cells 118 may not belimited to metals and may include other suitable materials or stack ofmaterials that can reflect and guide incoming visible light towardsradiation-sensing areas 104. In some embodiments of the presentdisclosure, bottom layer 122 of cells 118 is formed using a sputteringprocess, a plating process, an evaporation process, or any othersuitable deposition method. According to some embodiments of the presentdisclosure, the thickness of bottom layer 122 of each cell 118 can rangefrom about 100 Å to about 3000 Å (e.g., from 100 Å to 3000 Å).

Top dielectric layer 124 can include one or more dielectric layers. Insome embodiments, top dielectric layer 124 can protect previously-formedlayers of back side illuminated image sensor device 100 (e.g., bottomlayer 122 and capping layer 114). Top dielectric layer 124 can allowincoming light to pass through and reach radiation-sensitive areas 104.Top dielectric layer 124 can be made of a transparent material ormaterials. In some embodiments of the present disclosure, top dielectriclayer 124 can include SiO₂, Si₃N₄, SiON, or any other suitabletransparent dielectric material. Top dielectric layer 124 can bedeposited by CVD or ALD and can have a deposited thickness range fromabout 1000 Å to about 3000 Å (e.g., from 1000 Å to 3000 Å), according tosome embodiments. In some embodiments, composite grid structure 116includes more than two layers, such as a first layer of tungsten, asecond layer of plasma-enhanced oxide (PEOX) over the first layer, and athird layer of silicon oxynitride over the second layer.

Cells 118 also include a passivation layer 126, which is interposedbetween color filter 120 and the sidewalls materials of cells 118 (e.g.,bottom layer 122 and top dielectric layer 124). By way of example andnot limitation, passivation layer 126 can be conformally deposited by aCVD-based or an ALD-based deposition technique. Passivation layer 126can be formed from a dielectric material, such as SiO₂, Si₃N₄, or SiON,and can have a thickness between about 50 Å to about 3000 Å (e.g., from50 Å to 3000 Å).

According to some embodiments, the top surface of color filters 120 canbe aligned to the top surface of passivation layer 126 on top dielectriclayer 124. Alternatively, color filters 120 can be over the top surfaceof passivation layer 126 on top dielectric layer 124. For example andexplanation purposes, the top surface of color filters 120 will bedescribed as being aligned to the top surface of passivation layer 126on top dielectric layer 124.

After cells 118 of composite grid structure 116 receive their respectivecolor filters 120, a transparent material layer 128 can be formed overcomposite grid structure 116 and color filters 120. Transparent materiallayer 128 can be in contact with passivation layer 126 if the topsurface of color filters 120 is aligned to the top surface ofpassivation layer 126 over top dielectric layer 124, according to someembodiments. Alternatively, in some embodiments, transparent materiallayer 128 may not be in contact with passivation layer 126 if the topsurface of color filters 120 is above the top surface of passivationlayer 126 over top dielectric layer 124. In some examples, transparentmaterial layer 128 forms a micro-lens 130 over each cell 118 ofcomposite grid structure 116. Micro-lenses 130 are aligned withrespective radiation-sensing areas 104 and are formed so they cover thetop surface of color filters 120 within the boundaries of cell 118(e.g., within the side⁻walls of each cell 118).

Micro-lenses 130, due to their curvature, are thicker than other areasof transparent material layer 128 (e.g., areas between micro-lenses 130above top dielectric layer 124). For example, transparent material layer128 is thicker over color filter 120 (e.g., where micro-lens 130 areformed) and thinner in areas between micro-lenses 130 (e.g., above topdielectric layer 124)

Referring to FIG. 1, back side illuminated image sensor device 100 canalso include an interconnect structure 132. Interconnect structure 132can include patterned dielectric layers and conductive layers that forminterconnects (e.g., wiring) between radiation-sensing regions 104 andother components (not shown in FIG. 2). Interconnect structure 132 maybe, for example, one or more multilayer interconnect (MLI) structures134 embedded in an interlayer dielectric (ILD) layer 136. According tosome embodiments of the present disclosure, MLI structures 134 caninclude contacts/vias and metal lines. For purposes of illustration,multiple conductive lines 138 and vias/contacts 140 are shown in FIG. 1.The position and configuration of conductive lines 138 and vias/contacts140 can vary depending on design and are not limited to the depiction ofFIG. 1. Further, interconnect structure 132 can include sensing devices142. Sensing devices 142 can be, for example, an array of field effecttransistors (FETs) and/or memory cells that are electrically connectedto respective radiation-sensing areas (or pixels) 104 and configured toread an electrical signal produced in those areas as a result of alight-to-charge conversion process.

In some embodiments of the present disclosure, interconnect structure132 can be a top layer of a partially-fabricated integrated circuit (IC)or of a fully-fabricated IC that can include multiple layers ofinterconnects, resistors, transistors, and/or other semiconductordevices. As a result, interconnect structure 132 can include front endof the line (FEOL) and middle of the line (MOL) layers. Furthermore,interconnect structure 132 can be attached via a buffer layer (not shownin FIG. 1) to a carrier substrate (not shown in FIG. 1) that can providesupport to the structures fabricated thereon (e.g., interconnect layer132, semiconductor layer 102, etc.). The carrier substrate can be, forexample, a silicon wafer, a glass substrate, or any other suitablematerial.

In some embodiments of the present disclosure, fabrication of back sideilluminated image sensor device 100 can include forming semiconductorlayer 102 on a silicon substrate (e.g., silicon wafer) and subsequentlyforming interconnect structure 132 over front side 106 of semiconductorlayer 102. Interconnect structure 132 can undergo multiplephotolithography, etch, deposition, and planarization operations beforeit is completed. Once interconnect structure 132 is formed, a carriersubstrate (as discussed above) can be attached to the top ofinterconnect structure 132. For example, a buffer layer can act as anadhesion medium between the carrier substrate and interconnect structure132. The silicon substrate can be turned upside down, and the siliconsubstrate can be mechanically grinded and polished until back side 108of semiconductor layer 102 is exposed. The isolation structures on backside 108 of semiconductor layer 102 can be subsequently formed tofurther electrically isolate radiation-sensing areas or pixels 104.Capping layer 114, along with the composite grid structure 116, can beformed on back side 108 of semiconductor layer 102.

Composite grid structure 116 can be formed so that each of its cells 118is aligned to respective radiation-sensing areas or pixels 104.Alignment of composite grid structure 116 and radiation-sensing areas,or pixels, 104 can be achieved with photolithographic operations basedon, for example, alignment marks present on back side 108 ofsemiconductor layer 102. The formation of composite grid structure 116can include the deposition and subsequent patterning of bottom layer 122and top dielectric layer 124 using photolithography and etch operationsto form cells 118. Passivation layer 126 is subsequently deposited overthe exposed surfaces of bottom layer 122 and top dielectric layer 124.Color filters 120 can fill cells 118, and transparent material layer 128can be deposited thereon to form micro-lenses 130. Fabrication of backside illuminated image sensor device 100 is not limited to theoperations described above and additional or alternative operations canbe performed.

According to some embodiments, FIG. 3 is a flow chart of a method 300for forming one or more polarizing grating structures (grid polarizers)within the composite grid structure of an image sensor. For examplepurposes, method 300 will be described in the context of back sideilluminated image sensor device 100 of FIG. 1. The polarizing gratingstructure can have any of the following polarization directions: 0°,45°, 90°, or 135°. However, these directions are not limiting and otherpolarization directions are possible. Method 300 is not limited to backside illuminated image sensor devices and may be extended to other typesof image sensor devices, such as front side illuminated image sensordevices, that share similar material layers and/or geometries. Theseother types of image sensor devices are within the spirit and scope ofthe present disclosure.

According to some embodiments, method 300 can form grating elements incells 118 of composite grid structure 116. The grating elements can beoriented towards a polarization angle that can range from 0° to 135° atincrements of 45° (e.g., 0°, 45°, 90°, and 135°). Method 300 is notlimited to the operations described below. Other fabrication operationscan be performed between the various operations of method 300 and areomitted merely for clarity.

In referring to FIG. 3, method 300 begins with operation 302, where alayer stack is formed over a semiconductor layer. In some examples, thelayer stack can include more than 2 layers. FIG. 4 shows a partiallyfabricated image sensor, such as back side illuminated image sensordevice 100 of FIG. 1, according to method 300. In FIG. 4, and accordingto operation 302, a layer stack 400, which includes bottom layer 122 andtop dielectric layer 124, is formed over semiconductor layer 102. Asdiscussed above, bottom layer 122 can include titanium, tungsten,aluminum, or copper. However, bottom layer 122 is not limited to metalsand can include other suitable materials or stack of materials that canreflect and guide incoming visible light towards radiation-sensing areas104 of semiconductor layer 102. By way of example and not limitation,bottom layer 122 can be formed using a sputtering process, a platingprocess, an evaporation process, a chemical vapor deposition (CVD)process, an atomic layer deposition (ALD) process, or any suitabledeposition method. Further, the thickness of bottom layer 122 can rangefrom about 100 Å to about 3000 Å (e.g., from 100 Å to 3000 Å). Bottomlayer 122 is not deposited directly on semiconductor layer 102.According to some embodiments, bottom layer 122 is deposited overcapping layer 114. In some embodiments, bottom layer 122 may bedeposited on an adhesion/barrier layer disposed between bottom layer 122and capping layer 114. For simplicity, the adhesion/barrier layer is notshown in FIG. 4.

According to operation 302, and referring to FIG. 4, top dielectriclayer 124 of layer stack 400 can be deposited over bottom layer 122. Insome embodiments, top dielectric layer 124 can be a stack of one or moredielectric layers. In some embodiments, top dielectric layer 124 allowsincoming visible light to pass through. In other words, top dielectriclayer 124 is made of a transparent material, or materials, that functionas an anti-reflective material. In some embodiments, top dielectriclayer 124 is made of SiO₂, Si₃N₄, SiON, SiC, a polymer, or othersuitable transparent dielectric material(s). Top dielectric layer 124can be deposited by CVD or ALD and have an as-deposited thickness thatranges from about 1000 Å to about 3000 Å (e.g., from 1000 Å to 3000 Å).Alternatively, top dielectric layer 124 can be spin-coated on bottomlayer 122.

In referring to FIG. 3, method 300 continues with operation 304 and theformation of one or more polarization grating structures with gratingelements therein within a composite grid structure, such as compositegrid structure 116. In some embodiments, the formation of the one ormore polarization grating structures is performed concurrently with theformation of the composite grid structure, such as composited gridstructure 116. For example, referring to FIG. 4, a photoresist (PR)layer or a hard mask (HM) layer can be deposited over layer stack 400.The PR or HM layer is subsequently patterned so that patternedstructures 402 and 404 are formed over layer stack 400. Patternedstructures 402 can have a pitch P1 that ranges from about 100 nm toabout 500 nm (e.g., from 100 nm to 500 nm) and can be used to form thegrating elements of the polarization grating structures. The range ofpitch P1 ensures that the width of each grating element can range fromabout 20 nm to about 300 nm (e.g., from 20 nm to 300 nm), as discussedabove. Patterned structures 404 can have a pitch P2 greater than pitchP1 (e.g., P2>P1) and can be used to form the sidewalls of cells 118 ofcomposite grid structure 116. By way of example and not limitation, fourpatterned structures 402 and 404 respectively are shown in FIG. 4.However, additional patterned structures 402 and 404 are possible acrosslayer stack 400, according to some embodiments. Further, patternedstructures 402, which are responsible for the formation of the gratingelements of polarization grating structures, can be formed with theirlength at an angle with respect to patterned structures 404, which areresponsible for the formation of cells 118 in composite grid structure116. In some embodiments, the angle between patterned structures 402 and404 coincides with a polarization angle of visible light. In someembodiments, the polarization angle can range from 0° to 135° inincrements of 45°.

For example purposes, formation of grating elements will be describedwith patterned structures 402 being parallel to patterned structures 404(e.g., resulting in grating elements with a polarization angle of 0°).Based on the disclosure herein, other orientation angles, as discussedabove, can be implemented. These orientation angles are within thespirit and scope of this disclosure.

Patterned structures 402 and 404 are used as a mask layer so that asubsequent etch process can selectively remove layer stack 400 betweenpatterned structures 402 and 404 to form composite grid structure 116.In some embodiments, the etch process can use a different etch chemistryfor top dielectric layer 124 and bottom layer 122. In some embodiments,the etch process is end pointed; for example, it can be automaticallyterminated when capping layer 114 is exposed. Additionally, the etchprocess can be timed or can be a combination of timed and end-pointedetch processes. In some examples, the etch process is anisotropic sothat the etched features have nominally vertical sidewalls. Further theetch process can have high selectivity towards top dielectric layer 124and bottom layer 122. FIG. 5 is an example structure of FIG. 4 after theetch process of operation 304 described above.

Once the etch process is complete, patterned structures 402 and 404 canbe removed with a wet etch chemistry. The resulting etchedstructures—e.g., grating elements 600 and the sidewalls of cells 118—areshown in FIG. 6. In some embodiments, the height of grating elements 600is between about 200 nm and about 1000 nm (e.g., from 200 nm to 1000nm), their width is between about 20 nm and about 300 nm (e.g., from 20nm to 300 nm), and their pitch is between about 100 nm to about 500 nm(e.g., from 100 nm to 500 nm). In the example of FIG. 6, gratingelements 600 of polarization grating structure 610 are aligned parallel(e.g., at 0° polarization angle) to the sidewalls of cells 118 ofcomposite grid structure 116—as shown for example in FIG. 7a , which isa top view of polarization grating structure 610 within a cell 118 at 0°polarization angle. According to FIG. 6, polarization grating structure610 can be part of composite grid structure 116. In other words,polarization grating structure 610 can be formed in a cell 118 ofcomposite grid structure 116. As discussed above, grating elements 600can be aligned to different angles with respect to the sidewalls ofcells 118 so that polarization grating structure 610 can detect lightwith additional polarization angles. By way of example and notlimitation, FIGS. 7(a)-(d) are top views of exemplary polarizationgrating structures 610 with grating elements 600 oriented in differentangles with respect to the sidewalls of cell 118 (e.g., 0°, 45°, 90°, or135°). As discussed above, these angles can coincide with respectivepolarization angles of incident light.

Further, cells 118 of composite grid structure 116 and polarizationgrating structure 610 are substantially aligned to radiation-sensingregions 104 of semiconductor layer 102. Further, additional polarizationgrating structures are possible across composite grid structure 116.

In referring to FIG. 8, after the formation of grating elements 600 andcells 118, passivation layer 126 is conformally deposited over thesidewalls of cells 118 and grating elements 600. By way of example andnot limitation, passivation layer 126 can be deposited by a CVD-based oran ALD-based deposition method. Passivation layer 126 can be formed froma dielectric material, such as SiO₂, Si₃N₄, or SiON and can have athickness between about 50 Å to about 3000 Å (e.g., from 50 Å to 3000Å).

Referring to FIG. 3, method 300 continues with operation 306 where a gapbetween grating elements 600 of polarization grating structure 610 isfilled with a color filter, air, a dielectric material, or a combinationthereof. In some embodiments, the dielectric material is atransparent/anti-reflective material made of SiO₂, Si₃N₄, SiON, SiC, ora polymer.

In operation 308, cells 118 of composite grid structure 116 are filledwith one or more color filters 120, as shown in FIG. 9. In someembodiments, color filters 120 can be red, green, or blue. In theexample of FIG. 9, the gap between grating elements 600 is filled withair. FIGS. 10 through 13 show exemplary arrangements of color filters120 and polarization grid structures 610—with different polarizationangles—in composite grid structure 116, according to some embodiments.The examples of FIGS. 10-13 are not limiting and additional arrangementsare possible and within the spirit and the scope of this disclosure. Forexample, in a Bayern pattern—where the composite grid structure 116 caninclude 50% green color filters, 25% red color filters, and 25% bluecolor filters—some of the green color filters can be replaced bypolarization grating structures.

In referring to FIG. 9, a micro-lens 130 can be formed over each cell118 and polarization grating structure 610. Micro-lens 130 focuses theincoming light rays into respective cells 118 of composite gridstructure 116 towards radiation-sensing regions 104 of semiconductorlayer 102.

The present disclosure is directed to a method that describes theformation of a polarization grating structure (e.g., polarizer) as partof a composite grid structure of a back side illuminated image sensordevice. In some embodiments, the polarization grating structure can beintegrated into the composite grid structure by replacing one or morecolor filters of the composite grid structure with the polarizinggrating structure (grid polarizer). In some embodiments, the polarizinggrating structure can provide polarization information of the incidentlight along the following polarization directions: 0°, 45°, 90°, and/or135°. The aforementioned polarization directions are not limiting andother polarization directions are possible. According to someembodiments, the pitch between grating elements of polarizing gratingstructure can range from about 100 nm to about 500 nm (e.g., from 100 nmto 500 nm), and the width of each grating element can range from about20 nm to about 300 nm (e.g., from 20 nm to 300 nm). The grating elementsof the polarizing grating structure can be made of the same material asthe composite grid structure. Integration of the polarizers into thecomposite grid structure of a sensor device can offer several benefits,including: compact design for the image sensor, absence of moving parts,and faster acquisition of light polarization information (e.g.,polarization information for all polarization angles is collectedsimultaneously).

In some embodiments a semiconductor image sensor device includes asemiconductor layer with one or more sensing regions configured to senseradiation; a grid structure, over the semiconductor layer, with one ormore cells respectively aligned to the one or more sensing regions; anda polarizing grating in the one or more cells of the grid structureconfigured to polarize the light incoming to the semiconductor imagesensor.

In some embodiments a semiconductor image sensor includes one or morepolarizing grating structures with grating elements aligned to a lightpolarization angle, where the one or more polarization gratingstructures are disposed in cells defined by a grid structure; asemiconductor layer with sensing regions configured to sense radiationentering the semiconductor layer from the grid structure, where thesemiconductor layer is disposed below the grid structure so that each ofthe cells of the grid structure is aligned to a sensing region of thesemiconductor layer; and a micro-lens over each cell of the gridstructure.

In some embodiments a method to form an image sensor includes depositinga layer stack over a semiconductor layer with radiation-sensing regions,where the layer stack includes a bottom layer and a top anti-reflectivelayer. The method further includes, patterning the layer stack to form agrid structure with cells and a polarization grating structure within acell, where the polarization grating structure comprises gratingelements oriented to a light polarization angle. The method alsoincludes filling the grating structure between the grating elements withair or a dielectric material and filling the cells that do not contain apolarization grating structure with a color filter.

It is to be appreciated that the Detailed Description section, and notthe Abstract of the Disclosure, is intended to be used to interpret theclaims. The Abstract of the Disclosure section may set forth one or morebut not all exemplary embodiments contemplated and thus, are notintended to be limiting to the subjoined claims.

The foregoing disclosure outlines features of several embodiments sothat those skilled in the art may better understand the aspects of thepresent disclosure. Those skilled in the art will appreciate that theymay readily use the present disclosure as a basis for designing ormodifying other processes and structures for carrying out the samepurposes and/or achieving the same advantages of the embodimentsintroduced herein. Those skilled in the art will also realize that suchequivalent constructions do not depart from the spirit and scope of thepresent disclosure, and that they may make various changes,substitutions, and alterations herein without departing from the spiritand scope of the subjoined claims.

What is claimed is:
 1. A composite grid structure, comprising: a firstgroup of cells comprising a first color filter; a second group of cellscomprising a second color filter different from the first color filter;a third group of cells comprising a third color filter different fromthe first and second color filters, wherein cells from the first,second, and third groups are disposed next to each other; a first cellcomprising first grating elements aligned at a first angle; a secondcell comprising second grating elements aligned at a second angle; athird cell comprising third grating elements aligned at a third angle;and a fourth cell comprising fourth grating elements aligned at a fourthangle; wherein each of the first, second, third, and fourth angles aredifferent from each other and wherein the first, second, third, orfourth cells are disposed between the cells of the first, second, andthird groups.
 2. The composite grid structure of claim 1, wherein: thefirst with the second angles are supplementary; and the third with thefourth angles are supplementary.
 3. The composite grid structure ofclaim 1, wherein the first, second, third, and fourth cells are arrangedat a corner of the composite grid structure.
 4. The composite gridstructure of claim 1, wherein each of the first, second, third, andfourth cells are disposed between the cells of the first, second, andthird groups.
 5. A grating structure, comprising: a composite layer on asubstrate, wherein the composite layer comprises: a first layer on thesubstrate; and a second layer, different from the first layer, disposedon the first layer; openings in the composite layer traversing throughthe first and second layers, wherein the openings expose a portion ofthe substrate and form a plurality of grating elements on the substratespaced apart by the openings; and a capping layer disposed within theopenings and covering sidewall and bottom surfaces of the gratingelements and the exposed portion of the substrate.
 6. The gratingstructure of claim 5, wherein the first layer is a metal and the secondlayer is a dielectric layer.
 7. The grating structure of claim 5,wherein a space between two neighboring grating elements is betweenabout 100 nm and about 500 nm.
 8. The grating structure of claim 5,wherein the openings have a depth between about 200 nm and about 1000nm.
 9. The grating structure of claim 5, wherein the metal layercomprises tungsten, titanium, aluminum, or copper, and the dielectriclayer comprises silicon oxynitride, silicon nitride, silicon carbide,silicon oxide, or a polymer.
 10. The grating structure of claim 5,wherein the openings are filled with a dielectric material transparentto light.
 11. The grating structure of claim 5, the plurality of gratingelements are parallel to each other and are oriented at an angle 0°,45°, 90°, or 135° with sidewalk of the grating structure surrounding theplurality of grating elements.
 12. The grating structure of claim 5,wherein the plurality of grating elements form a light polarizer.
 13. Astructure, comprising: first and second cells arranged in a matrixconfiguration having horizontal rows and vertical columns; spaced apartgrating elements in the first cells, wherein the grating elements ineach first cell are parallel to each other, form an angle with sidewallsof the first cell, and comprise a stack of a first layer and a secondlayer; and a color filter in each cell of the second cells.
 14. Thestructure of claim 13, wherein the first layer comprises a metal layerand the second layer comprises a dielectric.
 15. The structure of claim13, wherein the first cells are located at a corner of the matrixconfiguration.
 16. The structure of claim 13, wherein the gratingelements have a height between about 200 nm and about 1000 nm.
 17. Thestructure of claim 13, wherein the color filter comprises red, blue, orgreen.
 18. The structure of claim 13, wherein the angle formed betweenthe grating elements and the sidewalls of the first cell is about 135°.19. The structure of claim 13, wherein a pitch between two neighboringgrating elements in the first cell is between 100 nm and about 500 nm.20. The structure of claim 13, wherein the grating elements and thesidewalls of the first cell have a substantially equal height.